Identification of video signals in a video system

ABSTRACT

Incoming digital video signals to a video system each undergo identification with specific identifier prior to receipt at a corresponding one of the video system inputs. At each of the video system outputs, the output signal undergoes decoding to obtain the identity of the signal to confirm proper routing of signals within the video system.

This application claims the benefit, under 35 U.S.C. §365 ofInternational Application PCT/US2006/046853, filed Dec. 8, 2006, whichwas published in accordance with PCT Article 21(2) on Jun. 12, 2008 inEnglish.

TECHNICAL FIELD

The invention relates to a technique for positive identification ofdigital video signals.

BACKGROUND ART

Identification of a serial digital video signal from a single source oreven a few sources generally presents little difficulties. However, in atypical broadcast facility, many serial digital video signals exist, andidentification of each signal often proves problematic, particularly asthe signals undergo routing through one or more devices, such as across-point switcher, some times referred to as a cross-point matrix.Presently, to positively identify a given serial digital video signalduring routing, descrambling and de-serialization of the signal mustoccur in order to decode the identification information. Carrying outthese processes requires a significant amount of hardware. Thus, in asystem having many serial digital video signals, providing the necessarydescrambling and de-serialization hardware often proves impractical froma cost, space and power consumption perspective. For this reason,broadcast facilities typically rely completely on routing control systemstatus information to determine which input connects to a given outputin the cross-point matrix. Such reliance incurs the disadvantage that noautomated method exists for checking the actual signal present at agiven cross-point matrix output and alerting the user should the statusinformation prove erroneous.

BRIEF SUMMARY OF THE INVENTION

In accordance with an illustrative embodiment of the present principles,a method for identifying a digital video signal in a video systemcommences with the step of phase modulating the digital video signalwith an identification signal at an input of the video system, therebyidentifying that signal. The phase modulated digital video signalundergoes demodulation at an output of the video system to establish theidentity of the video signal. In this way, verification of properrouting of the signal through video system can occur.

BRIEF SUMMARY OF THE DRAWINGS

FIG. 1 depicts a block schematic diagram of video system that identifiesat least one digital video signals at an input for confirmation at anoutput in accordance with an illustrative embodiment of the presentprinciples,

FIG. 2 depicts a block schematic diagram of one of the input circuits ofthe video system of FIG. 1 to phase modulate an input signal to identifythat signal;

FIG. 3 depicts a block schematic diagram of one of the output circuitsof the video system of FIG. 1 to demodulate an output signal for obtainthe identification of that signal.

DETAILED DESCRIPTION

As described in greater detail hereinafter, in accordance with thepresent principles, the digital video input signal to a video system,gets identified to enable verification of signals at the system outputs.

FIG. 1 depicts a video system 10 which illustratively takes the form ofcross-point matrix, some times referred to as a cross-point switcher orrouter, having the capability of routing a digital video signal at oneor more of its inputs 12 ₁-12 _(n) to one or more of its outputs 14 ₁-14_(m) where n and m are both integers greater than zero, but notnecessarily equal to each other. The cross-point matrix 10 performs therouting of selected signals at its respective inputs 12 ₁-12 _(n) toselected ones of the outputs 14 ₁-14 _(m) under control of a routingcontrol system (not shown). For a large video cross point matrix where nand m are both large, confirmation of the routing of a digital videosignal from an input to any given output previously depended on statusinformation provided by cross-point matrix or its control system. Sinceno mechanism heretofore existed for independent signal identification,an error in the status information thus could go undetected.

In accordance with the present principles, the cross-point matrix 10 hasa plurality of input circuits 16 ₁-16 _(n) coupled to corresponding onesof the matrix inputs 12 ₁-12 _(n), respectively. Each input circuit suchas input circuit 12 ₁ receives an incoming serial digital video signaldestined from the cross-point matrix 10 and provides the signal with itsown identification in a manner described hereinafter. In this way, eachinput signal routed through the cross-point matrix 10 to one or moreoutputs 14 ₁-14 _(m) carries its own unique identifier.

Each of the cross-point matrix 10 outputs 14 ₁-14 _(m) is coupled to acorresponding output circuit 18 ₁-18 _(m), respectively. Each outputcircuit, such as output circuit 18 ₁ serves to strip the identifier fromthe signal at the corresponding cross point matrix output. Theidentifier stripped from the output signal is decoded to verify that theoutput signal corresponds to the input signal routed from the intendedinput. In other words, if the signal at input 12 ₁ was to be routed tooutput 14 ₁, the identifier associated with the output signal appearingat that output should match the identifier of the input signal at thecorresponding cross-point matrix input. Thus, the combination of theinput circuits 16 ₁-16 _(n) and output circuits 18 ₁-18 _(m) provide amechanism for determining whether an error exists in the cross-pointmatrix 10 status information.

FIG. 2 depicts a block diagram of an exemplary input circuit, such asinput circuit 16 ₁, all of which share the same features. The inputcircuit 16 ₁ includes an equalizer and re-clocking circuit 20 forequalizing and re-clocking an incoming serial digital video signal. Aphase modulator 22 phase modulates the output signal of the equalizerand re-clocking circuit 20 with a source identification informationsignal specific to the particular input circuit. In other words, each ofthe input circuits 16 ₁-16 _(n) makes use of a different sourceidentification information signal to uniquely identify each incomingserial digital video signal.

The frequency of each source identification signal typically will lieabove the pass band of a loop filter (not shown) in the output of theequalizer and re-clocking circuit 20. In practice, the loop band passbandwidth usually lies in the 100-200 kHz region. The frequency of thesource identification signal is also chosen so that it is not an integersub-multiple of the serial digital video data rate (i.e. 135 MHz, 90MHz, 67.5 Hz etc. for a 270 Mb/s signal or 742.5 MHz, 495 MHz, 371.25MHz etc. for a 1.485 Gb/s signal). Avoiding such frequencies avoids thelarge amounts of energy present at these frequencies in the serialdigital video signal frequency spectrum. The depth of modulation is setso that the combined total of phase modulation and jitter from othersources is less than 20% of the unit interval for the data rate used.Setting the depth of modulation in this manner assures that signalrecovery can occur without error by during re-clocking by one of theoutput circuits 18 ₁-18 _(m).

FIG. 3 depicts an exemplary output circuit, such as circuit 18 ₁, all ofwhich share the same features. The output circuit 18 ₁ includes are-clocking flop-flop register 24 supplied at its D input with theserial digital video signal from the associated output of thecross-point matrix 10 of FIG. 1. A phase detector 26 within the outputcircuit 18 ₁ also receives the serial digital video signal at a firstinput from the cross-point matrix 10 of FIG. 1. The phase detector 26has its second input supplied with the output signal of a voltagecontrolled oscillator 27 which serves as the clock signal generator forthe re-clocking register 24.

The phase detector 26 provides an output signal in accordance with thephase difference between the signals at its first and second inputs toboth a loop filter 28 and a source identification decoder 30. The sourceidentification signal decoded by the decoder 30 allows the routingcontrol system for the cross-point matrix 10 (not shown) to verify thecorrect routing path through the cross-point matrix. The sourceidentification signal has a higher frequency than the pass band of theloop filter 28 so that the loop filter effectively rejects the sourceidentification signal. In this way, the voltage controller oscillator27, driven at its input by the output signal of the loop filter 28, willnot track the source identification signal.

As indicated previously, the output signal of the voltage controlledoscillator 27 serves as the clock signal for the re-clocking register24. With the loop filter 28 filtering out the source identificationsignal from the voltage controlled oscillator 27, the sourceidentification effectively gets removed from the output of there-clocking register 24. In this way, the re-clocking register 24 candrive an output buffer 36 with re-clocked signal corresponding to theincoming serial digital video signal in a normal manner.

The foregoing describes a technique for identifying serial digital videosignals in a video system, thereby enabling verification of the routingof such signals through the video system.

The invention claimed is:
 1. A method for identifying a digital videosignal in a video system, comprising the steps of: phase modulating anincoming digital video signal with an identification signal at an inputof the video system to identify the digital video signal, wherein thevideo system is a cross-point matrix, wherein the frequency of theidentification signal lies above a passband of a loop filter in anoutput of an equalizer and re-clocking circuit and the frequency of theidentification signal is chosen so as not to be an integer sub-multipleof the serial digital video rate, and further wherein the phasemodulation is set so that a combined total of the phase modulation andjitter from other sources is less than a predetermined percentage of aunit interval for the serial digital video rate; and demodulating thephase modulated digital video signal at an output of the video system toyield the identity of the digital video signal.
 2. The method accordingto claim 1 wherein the step of phase modulating includes the step ofequalizing and re-clocking the incoming digital video signal prior tophase modulation.
 3. The method according to claim 1 wherein theidentification signal has a frequency that differs from an integermultiple of a data rate of the incoming digital video signal.
 4. Themethod according to claim 1 wherein the demodulating step comprises thesteps of: generating a difference signal in accordance with phasedifference between the phase-modulated digital video signal at the videosystem output and an oscillator output signal; filtering the differencesignal; varying the oscillator output signal in accordance with thedifference signal; and decoding the difference signal to obtain theidentity of the digital video signal.
 5. A video system having at leastone input and output comprising: at least one input circuit coupled tothe at least one video system input for receiving an incoming digitalvideo signal and for processing the video signal to add an identifierthereto, wherein the video system is a cross-point matrix, wherein thefrequency of the identification signal lies above a passband of a loopfilter in an output of an equalizer and re-clocking circuit and thefrequency of the identification signal is chosen so as not to be aninteger sub-multiple of the serial digital video rate, and furtherwherein the phase modulation is set so that a combined total of thephase modulation and jitter from other sources is less than apredetermined percentage of a unit interval for the serial digital videorate; and at least one output circuit coupled to the at least one videosystem output for decoding a digital video signal at the at least onevideo system output to obtain the identifier with the incoming digitalvideo input signal.
 6. The video system according to claim 5 wherein theat least one input circuit comprises: an equalizing and re-clockingcircuit for equalizing and re-clocking the incoming digital videosignal; a phase modulator for phase modulating the equalized andre-clocked incoming digital video signal with an identification signalspecific thereto.
 7. The video system according to claim 6 wherein theat least one output circuit comprises: voltage controlled oscillator;means for generating a difference signal in accordance with phasedifference between the phase-modulated digital video signal at the videosystem output and an output signal of the voltage controlled oscillator;means for filtering the difference signal to yield an output signal thatdrives the voltage controlled oscillator; and means for decoding thedifference signal to obtain the identity of the digital video signal. 8.The video system according to claim 6 wherein the identification signalhas a frequency above a passband of the loop filter in a re-clockingphase-locked loop.
 9. The video system according to claim 6 wherein theidentification signal has a frequency that differs from an integermultiple of the data rate of the incoming digital video signal.